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Wheat Growers Should Not Forget About Hessian Flies

August 28, 1998

While glancing at the fall 1998 (vol. 4, no. 4) issue of the Illinois Wheat Association Newsletter, I came across an article about Hessian flies written by Roger Ratcliffe, research entomologist, USDA-ARS, West Lafayette. Roger is a recognized expert on Hessian flies and resistant wheat varieties, and he has been monitoring Hessian fly populations in southern Illinois for many years. I think his observations are important, so Ill excerpt some of them from the article.

One of the main reasons Roger and his associates monitor Hessian fly populations is to assess the specific biotypes of the insects collected. "Biotypes of the Hessian fly become prevalent in the field in response to exposure to resistant wheat varieties. Over a period of 6 to 8 years of continual exposure to wheat varieties carrying specific genes for resistance, fly populations change so that new virulence genes become prevalent and render the resistance ineffective.

"All Hessian fly populations collected from southwestern Illinois during this period (19951998) were largely biotype L (84 to 100 percent), with a low frequency of biotypes D and G. Illinois counties represented in these collections were Alexander, Franklin, and Randolph; however, it is likely that Hessian fly populations throughout the soft winter wheat area of Illinois would be very similar in composition. Hessian fly populations in the southernmost Illinois counties may still contain low frequencies of biotype D, but this would have little influence on the effectiveness of resistance genes currently available in wheat varieties adapted to the area. Resistance gene H5 is effective against biotype D, but the percentage of D is so low in field populations that wheat varieties carrying H5 resistance would be largely ineffective."

Roger's findings of a predominance of biotype L in Illinois populations of Hessian flies are quite important. "Biotype L has the ability to infest and injure wheat varieties that carry one or more of the four resistance genes that presently are available in soft winter wheat varieties. Thus, the resistant wheat varieties presently available to Illinois wheat growers are largely ineffective in controlling the Hessian fly. Fortunately, fly populations have remained low enough that little injury occurs in most fields, but the potential for more severe injury is present. This makes it very important for growers to utilize cultural practices that help reduce exposure of wheat to high fly populations. Two cultural control methods that are effective are seeding wheat after the peak emergence period of the fly in the fall (fly-free date) and destruction of volunteer wheat that serves as an over-summering site for flies that develop to the pupal or flaxseed stage in the spring and emerge as adults in the fall."

Roger and his colleagues have developed a new soft red winter wheat variety that is resistant to Hessian fly biotype L. However, it probably won't be available for planting until the fall of 1999. Therefore, it is important that wheat growers seriously consider the cultural tactics of keeping densities of Hessian flies low. We encourage all wheat growers to plant wheat in 1998 after the fly-free dates that are provided in Table 1 for all counties of Illinois. Implementation of this cultural practice in 1998 could prevent economic losses in 1999.

Table 1. Average date of seeding wheat for the highest yield.

County Average date of seeding wheat for the highest yield County Average date of seeding wheat for the highest yield
Adams Sept. 30-Oct. 1 Lee Sept. 19-21
Alexander Oct. 12 Livingston Sept. 23-25
Bond Oct. 7-9 Logan Sept. 29-Oct. 3
Boone Sept. 17-19 Macon Oct. 1-3
Brown Sept. 30-Oct. 2 Macoupin Oct. 4-7
Bureau Sept. 21-24 Madison Oct. 7-9
Calhoun Oct. 4-8 Marion Oct. 8-10
Carroll Sept. 19-21 Marshall-Putnam Sept. 23-26
Cass Sept. 30-Oct. 2 Mason Sept. 29-Oct. 1
Champaign Sept. 29-Oct. 2 Massac Oct. 11-12
Christian Oct. 2-4 McDonough Sept. 29-Oct. 1
Clark Oct. 4-6 McHenry Sept. 17-20
Clay Oct. 7-10 McLean Sept. 27-Oct. 1
Clinton Oct. 8-10 Menard Sept. 30-Oct. 2
Coles Oct. 3-5 Mercer Sept. 22-25
Cook Sept. 19-22 Monroe Oct. 9-11
Crawford Oct. 6-8 Montgomery Oct. 4-7
Cumberland Oct. 4-5 Morgan Oct. 2-4
DeKalb Sept. 19-21 Moultrie Oct. 2-4
DeWitt Sept. 29-Oct. 1 Ogle Sept. 19-21
Douglas Oct. 2-3 Peoria Sept. 23-28
DuPage Sept. 19-21 Perry Oct. 10-11
Edgar Oct. 2-4 Piatt Sept. 29-Oct. 2
Edwards Oct. 9-10 Pike Oct. 2-4
Effingham Oct. 5-8 Pope Oct. 11-12
Fayette Oct. 4-8 Pulaski Oct. 11-12
Ford Sept. 23-29 Randolph Oct. 9-11
Franklin Oct. 10-12 Richland Oct. 8-10
Fulton Sept. 27-30 Rock Island Sept. 20-22
Gallatin Oct. 11-12 St. Clair Oct. 9-11
Greene Oct. 4-7 Saline Oct. 11-12
Grundy Sept. 22-24 Sangamon Oct. 1-5
Hamilton Oct. 10-11 Schuyler Sept. 29-Oct. 1
Hancock Sept. 27-30 Scott Oct. 2-4
Hardin Oct. 11-12 Shelby Oct. 3-5
Henderson Sept. 23-28 Stark Sept. 23-25
Henry Sept. 21-24 Stephenson Sept. 17-20
Iroquois Sept. 24-29 Tazewell Sept. 27-Oct. 1
Jackson Oct. 11-12 Union Oct. 11-12
Jasper Oct. 6-8 Vermilion Sept. 28-Oct. 2
Jefferson Oct. 9-11 Wabash Oct. 9-11
Jersey Oct. 6-8 Warren Sept. 23-27
JoDaviess Sept. 17-20 Washington Oct. 9-11
Johnson Oct. 10-12 Wayne Oct. 9-11
Kane Sept. 19-21 White Oct. 9-11
Kankakee Sept. 22-25 Whiteside Sept. 20-22
Kendall Sept. 20-22 Will Sept. 21-24
Knox Sept. 23-27 Williamson Oct. 11-12
Lake Sept. 17-20 Winnebago Sept. 17-20
LaSalle Sept. 19-24 Woodford Sept. 26-28
Lawrence Oct. 8-10  

Author: Kevin Steffey